Method for connection of secure conference calls

ABSTRACT

The present invention provides a method and apparatus of making secure conference calls in which the bridging unit does not need to know any encryption keys and can function independently of the encryption process used by the communicating parties. This means that there is no security requirement for the conference unit, there are fewer restrictions on where it can be placed, and it does not introduce any additional weaknesses in the security system.

FIELD OF THE INVENTION

This invention relates to audio teleconferencing but more particularlyto a secure conference network and method of connection thereof.

BACKGROUND OF THE INVENTION

One service that is required in a communication network is audioteleconferencing. This service allows a number of callers to talktogether from a number of separated telephone instruments. In a secureconference call, two additional features are provided. The speech passedbetween the parties is encrypted, using keys known only to the senderand the receiver, so that the speech is not understandable by anyeavesdropper who intercepts the call. In addition the parties incommunication are authenticated so that each is assured of the identityand clearance level of the others.

To provide the conference feature, a bridge circuit is often employed.This circuit combines the signals from all parties and distributes theresults to each listener. Unfortunately when the speech is encrypted thebridge circuit can no longer sum the signals as the encryption istypically a non-linear process.

In past implementations of secure conference circuits, the bridge wouldfirst decrypt the incoming signals, then sum the resulting clear speech,then encrypt the result and distribute it to all parties in theconference. This method requires the bridge circuit to know theencryption keys for all parties and clear speech signals are containedwithin the unit. This means that the conference bridge itself must beconsidered as a part of the security system. This introduces anotherpoint of weakness in the system and some users may not wish to trust thesecurity of a bridge operating outside their direct control. It is thusdesirable to make a conference unit that can operate without requiringrecourse to clear speech.

Another approach to this problem has been described in a paper byBrickell et al. CRYPTO '87 Proceedings, entitled "Secure AudioTeleconference". In this method, an encryption process is used withcertain linear properties which allows the bridge circuit to sum thesignals in a normal manner for distribution. Unfortunately this limitsthe number of applicable encryption techniques and not all users wouldbe willing to trust these schemes. This method also restricts the speechcoding techniques allowed, produces some bandwidth expansion, andrequires some synchronization (in time) of the signals from all of theconferees.

It is thus desirable to design a method and apparatus which can functionindependently of the encryption process being used and also does notsuffer from the above mentioned limitations.

SUMMARY OF THE INVENTION

The primary object of the present invention is to provide a method andapparatus of making secure conference calls in which the bridging unitdoes not need to know any encryption keys and can function independentlyof the encryption process used by the communicating parties. This meansthat there is no security requirement for the conference unit, there arefewer restrictions on where it can be placed, and it does not introduceany additional weaknesses in the security system.

DESCRIPTION OF THE DRAWINGS

Particular embodiments of the invention will be understood inconjunction with the accompanying drawings in which:

FIG. 1 is an illustrative block diagram of a secure conference systemaccording to a first embodiment of the present invention;

FIG. 2 is an illustrative block diagram of the conference system of FIG.1 according to a further embodiment of the present invention;

FIG. 3 is a block diagram of a secure telephone set used in the secureteleconference network of the present invention;

FIG. 4 is a block diagram of the signal processing operation used in thesecure telephone set of FIG. 3;

FIG. 5 is an illustrative block diagram of a secure telephone setaccording to a second embodiment of the present invention; and

FIG. 6 is a block diagram of an alternate conference network accordingto another embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to FIG. 1, we have shown generally at reference numeral 10an illustrative block diagram of the conference system of the presentinvention. The system is basically comprised of a conference controlunit 11, a number of telephone sets A, B, C, and D and a switchingnetwork 12. Each telephone set has two channels for connection to theswitches. These channels may be multiplexed on a single physicalconnection. The network 12 may consist of a number of nodes or switchingcenters connected by transmission facilities. End to end digitalconnectivity should be provided through the use of the digitalsubscriber access technology and a digital network or an analog networkcombined with voice band modems.

For example, in FIG. 1, switching network 12 is comprised of telephoneswitches A, B, C and D. Each switch may be connected to another switchby means of trunk lines 13, 14 and 15. In FIG. 1, telephone sets A, B, Cand D are each connected to their own switch, i.e. switch A, B, C and D.However, it will be known to those knowledgeable in the art that anumber of telephone sets within the teleconference network may beinterconnected via the same switch. The number of switches will ofcourse depend on the location of teleconference users. For example, setsA and B could be interconnected via the same switch if these are locatedin the same office or local area network. These switches can be anytypical telephone switches supporting digital loops on voice band datamodems such as the DMS-100 (trademark) switch.

A DMS-100 is currently adaptable to provide the conference control unit.

In FIG. 1, four parties are connected in a teleconference network.However, any number of parties can be connected in a similar manner. Toform the conference, the parties are connected together by means of theswitching network 12 under the control of the conference control unit11. This connection pattern is established by having a first partyinitiate the conference call feature. In this example, channel 2 ofphone A connects to channel 1 of phone B, channel 2 of phone B connectsto channel 1 of phone C, and channel 2 of phone C connects to channel 1of phone D, see FIG. 2. Note that channel 1 of phone A and channel 2 ofphone D are not used. As the channels to each phone are interchangeable,the designations channel 1 and channel 2 could be reversed on the phoneswithout affecting the operation of the system. Once this connectionpattern has been established, each phone can then initiate a secure callwith a connected neighbor using the encryption process of their ownchoice. Once the secure calls are established on each channel the signalprocessing circuits of phones B and C will operate to combine the speechfrom each active channel and the user speech and to distribute it toother channels and the user. The speech or messages from each phone useris thus heard at all other phones in the conference. The voice fromphone A, for example, is heard at phone D after passing though phones Band C.

Because of the digital techniques used in the switching network and thetransmission lines, there will be no practical accumulation of noise todegrade the speech signal. Quantization noise does not accumulate withsuccessive codings in the chain if conferencing and coding functions arepartitioned properly. This results in synchronous coding at each stationand is practical with the common pulse code modulation (PCM), adaptivedifferential PCM (ADPCM) and the CCITT standard wide band audio (WBA)coding schemes.

The telephone sets in this arrangement are connected to the network inthe manner of ordinary telephone sets. However, in the most practicalarrangement, digital communication techniques are used for access,transmission and switching. The method can still be applied to an analogor a mixed analog/digital switching/transmission network if suitable lowbit rate speech coding and voice band data modems are employed toprovide digital signals for use by the secure telephone sets. Note thatthese modems can be incorporated within the secure telephone sets topermit the conference method to operate on either analog or digitalnetworks.

The conference control unit 11 acts to set up and supervise theinterconnection between the secure telephones to form the conference.The role of the conference control unit 11 is to request connections inthe switching network 12. No processing of speech by the conference unitor by the network is needed. The secure conference feature is madepossible by having each secure telephone set connected to the switchingnetwork 12 with two or more logical channels depicted generally atreference numeral 16. This may be done practically in a number of ways.It is possible to simply use two pairs of wires for each set and thenmake two network connections as shown in FIGS. 1 and 2. It is alsopossible to combine two logical communication channels on a single pairof wires or network connection by the use of speech coding techniqueswhich multiplex a number of channels as shown in FIG. 6.

ISDN (Integrated Services Digital Network), for example, supports twofull speech channels (64 Kb/s each) and one data channel (16 Kb/s) for atotal of 144 Kb/s on a single standard telephone wire pair. ISDN thusdirectly supplies two logically separate speech channels on a singlesubscriber pair.

Referring now to FIG. 3, we have shown a block diagram of a securetelephone set used with the teleconference system of FIGS. 1 and 2. Inthis embodiment, the two logical connections 20 and 21 from the set tothe switching network 12 are labelled channel 1 and channel 2respectively. These channels are connected to encryption/decryptioncircuits 22 and 23 respectively. These are used to encrypt the messagesor speech sent and decrypt those received over each logicalcommunications channel.

A description of speech encryption/decryption techniques which may beused with this invention is disclosed in a paper by W. Diffie et al.,Third Annual Symposium on Physical/Electronic Security, August 1987,entitled "Secure Communications with the Integrated Services DigitalNetwork (ISDN)".

The encryption/decryption circuits 22 and 23 are connected to speechcoding/decoding circuits 24 and 25, respectively. These may operateunder any suitable coding scheme. Although some coding schemes mayresult in excessive coding delay, there are practical coding schemes,notably companded PCM, ADPCM, and the CCITT wideband audio standard,where the coding delay is insignificant.

The two coding/decoding circuits 24 and 25 are connected to anauthentication, control and signal processing circuit 26 (ACSP). Thiscircuit performs several functions. One operation is to connect the useroutput and input signals 27 and 28 of the microphone 29 and speaker 30forming part of user interface 31, to the communication channels viaencryption circuits 22 and 23. The circuit also acts to perform thesecurity authentication tasks, to activate the encryption circuits 22and 23 and to provide them with encryption keys.

The ACSP circuit 26 can perform signal processing tasks involving thespeech decoded from the two logical communication channels 20 and 21 anduser interface 31. This signal processing involves, for example, summingthe decoded speech and presenting the sum to the user interface 31 to beheard over speaker 30. The signal from the user interface would bemonitored with a speech detector. U.S. Pat. No. 4,410,763 which issuedto applicant describes such a speech detector. If the detectordetermines the signal to be speech, then this signal would be summedwith the signals sent to the communications channels. These threesumming operations form a simple three-party conference bridge.

The operations discussed above performed by the circuits 22 through 26are illustrated in FIG. 4. The ACSP circuit consists of three adders 41,42 and 43, a speech detector, code translation and automatic gaincontrol circuit 44 connected at the output 45 of the user interface 46and a code translation circuit 47 connected at the input 48 of the userinterface.

The incoming signal received at the input 49 of logical channel 1 isfirst decrypted at decryption circuit 50 and then decoded at decodingcircuit 51. Similarly, the incoming signal received at the input 52 oflogical channel 2 is first decrypted at decryption circuit 53 and thendecoded at decoding circuit 54. The resulting linear speech signalsreceived from channels 1 and 2 are forwarded to adder 42. The sum ispresented to the input 48 of user interface 46 through code translationcircuit 47 to be heard on speaker 55. The translation of signals may berequired if for example, the unit uses a mu-law codec, then the linearsum will need to be mu-law encoded before being sent to the codec todrive loudspeaker 55. Similarly the output 4 from microphone 56 wouldneed to be translated to linear form by code translation circuit 44 if,for example, a mu-law codec was used.

Adder 41 is used to add the speech signal from input 52 of channelnumber 2 with a speech signal detected from the output 45 of userinterface 46. If the speech detecting circuit 44 detects a speechsignal, it is summed by adder 41 with the incoming speech signalreceived at the input 52 of logical channel 2 and presented first tocoding circuit 57 and then to encryption circuit 58 for transmission atoutput 59 of logical channel 1. Similarly, adder 43 will add a detectedspeech signal from microphone 56 with an incoming speech signal receivedfrom input 49 of logical channel 1. The sum will be coded and acceptedby circuits 60 and 61 respectively and appear as the outgoing signal atoutput 62 of logical channel 2. The automatic gain control circuit 44would be used to adjust the signal level of the speech from themicrophone 56 to attain a uniform volume level for the conference.

The use of automatic gain control (AGC) in teleconferencing is describedin a paper by John Ellis and Bruce Townsend in TELESIS 1987 ONE, pages23-31, entitled "Conference Bridge: State of the Art inTeleconferencing".

If speech coding is being used, and the speech detector indicates nouser input from microphone 56, then the signals from the channels neednot be decoded and recoded to be passed between channels.

In some cases different speech coding rules may be used by differentsets that wish to be included in a conference. For example, some phonesmay use mu-law PCM speech coding while others may use A-law PCM coding.These different terminal types could be accommodated in this conferencemethod in the following way. In FIG. 1, if telephone sets A and B usedthe mu-law coding technique and telephone sets C and D used the A-lawcoding technique, then they would be connected as shown with groups oflike terminals connected together. Telephone set C (or possiblytelephone set B) will then operate its signal processing circuit toperform a translation between the two coding types as part of itsconference summing operations. The separate parts of the conference arethus able to communicate with the other through the translationcapabilities of one of the telephone sets.

Perhaps some terminals may use the CCITT wide band audio standard. Thisaudio standard is described in a paper by P. Mermelstein in IEEECommunications, Volume 26, No. 1, Jan. 88, and is entitled "A New CCITTCoding Standard for Digital Transmission of Wideband Audio Signals".

In a wide band audio terminal application, the code translation circuits44, 47 of FIG. 4 would include the analysis and synthesis quadraturemirror filters (QMF). The coding/decoding circuits 51, 54, 57, 60 handlethe low sub-band and high sub-band components. The pair of low and highband components of the signal are summed separately. This method ispreferable to avoid accumulation of delay in QMF filters and to preventaccumulation of quantization noise.

When mixing narrow band and wide band terminals, the narrow bandterminals should first be converted to wide band.

Referring now to FIG. 5, we have shown an illustrative block diagram ofa secure telephone set according to a second embodiment of the presentinvention. In particular, this set can be used when a single physicalconnection is used to connect the telephone set to the switchingnetwork. In this embodiment, an ACSP circuit 70 is connected to userinterface 71 and the two speech channels 72 and 73 are connected tospeech coding/decoding circuits 74 and 75. These are connected toencryption/decryption circuits 76 and 77 respectively, to permit theencryption of the two speech channels.

Once coded and encrypted, the logical channels can then be combined bymeans of a multiplexing circuit 78 and forwarded to a switching networkvia a single communication path 79.

For example, this could involve using the CCITT ADPCM algorithm in thecoder/decoder 74, 75 to provide two 32 Kb/s speech signals which can becombined by multiplexer 78 (after encryption) onto one standard 64 Kb/schannel. Using multiplexing techniques of this sort permits the securephone and the conference feature to be implemented easily within theexisting communications networks.

Referring now to FIG. 6, we have shown an illustrative block diagram ofan alternate conference network for use with the secure telephone set ofFIG. 5. In particular, each set is connected to a switch via a singleaccess channel. In this arrangement, the role of the conference controlunit 80 also includes the demultiplexing of each input channel into twological channels and the redistribution and multiplexing of these amongthe participants. For example a single 64 Kb/s channel would demultiplexinto two 32 Kb/s logical channels.

In principle, it is possible for one encryption process to be used, forexample, between phones A and B, but a different process could be usedbetween B and C if they so choose (see FIG. 1). This permits flexibilityin the types of terminals used with the system. Also it can be notedthat if a symmetric key encryption technique is being used, it ispossible to use different encryption keys on each segment of theconference circuit. If this is done, then the bit patterns on the twochannels to a secure telephone set will be different even if the userhas no input i.e. is not speaking. An eavesdropper would thus be unableto determine which party of the conference is speaking. This may beconsidered an additional security feature by some users. Otherwise it ismost practical for all segments of the conference to be encrypted withthe same key. As the entire conference can be decoded by breaking thecryptosystem on any one link between users, there is no advantage inhaving separate keys for each link.

With this arrangement, the clear text or speech appears only at thetelephone sets where it must appear anyway for the user. Thus there isno additional security weakness in the system due to the presence of theconference feature. The conference control unit 11 is responsible foradministering the connections between the parties but it does not needto know any encryption keying information or operate on any clear text.The encryption and authentication process is all under the directcontrol of the user's secure telephones and they need not trust theconference unit with any of their security information.

With this method, if one party wishes to drop out of the conference,then it is the responsibility of the conference control unit 11 toreconnect the remaining parties by instructing the communication andswitching network 12. For example, in FIG. 2, if phone C wished to dropout of the conference, then the conference unit would instruct thenetwork to reconnect channel 2 of phone B to channel 1 of phone D. Thesetwo phones would then reinitiate a secure call between themselves, afterthis was established, the conference could continue among the remainingphones i.e. phones A, B and D.

If another party wished to be included in the conference, then theconference unit would instruct the network to connect channel 2 of phoneD to channel 1 of the new party. These two phones would then initiate asecure call and the new party would be included in the conference.

As is customary in conference calls, one party or an operator, acts as acontroller to administer the conference and issue the instructions tothe conference unit to include or remove parties from the conference.This conference manager would communicate with the conference controlunit using a separate logical communication channel established betweenthe manager and the conference unit. As an option, this communicationchannel could be secure. The conference manager would also beresponsible for authenticating the identities of all participants in theconference and perhaps also distributing the identities of theparticipants to all of the conferees. A number of techniques known inthe art can be used for this and need not be discussed further. Othertechniques can also be used in which every party performs his ownauthentication of every other party in the conference.

A secure conference network could also be provided by interconnectingusers through two or more conference control units in geographicallyseparated regions.

What is claimed is:
 1. A method of bridging teleconference calls at eachtelephone set used within a teleconference network, comprising the stepsof:receiving a first incoming signal from a first adjacentteleconference user via a first logical channel; decoding said firstincoming signal to provide a first incoming speech signal; forwardingsaid first incoming speech signal to a first input of a signalprocessing circuit means; receiving a second incoming signal from asecond adjacent teleconference user via a second logical channel;decoding said second incoming signal to provide a second incoming speechsignal; forwarding said second incoming speech signal to a second inputof said signal processing circuit means; detecting the presence of anddecoding a user's output speech signal from an output of user interfacemeans; forwarding said output speech signal if present to a third inputof said signal processing circuit means; summing said speech signals ofsaid first and second inputs at said signal processing means andforwarding the summed signal to an input of code translation circuitmeans for conversion and forwarding to an input of said user interfacemeans; summing said speech signals of said second and third inputs atsaid signal processing means to provide a first outgoing speech signal;coding said first outgoing speech signal to provide a first outgoingsignal; transmitting said first outgoing signal to said first adjacentuser via said first logical channel; summing said speech signals of saidfirst and third inputs at said signal processing circuit means toprovide a second outgoing speech signal; coding said second outgoingspeech signal to provide a second outgoing signal; and transmitting saidsecond outgoing signal to said second adjacent user via said secondlogical channel.
 2. A method as defined in claim 1 further comprisingthe step of instructing said communications network having switchingnodes and transmission links to establish a chain-like connectionpattern between said teleconference users such that each telephone setis connected to an adjacent set allowing each user to communicate withan adjacent user.
 3. A method as defined in claim 2 wherein saidcommunications network is instructed to establish a chain-likeconnection pattern between said teleconference users by connecting thetelephone set of a user to a telephone set of a first adjacentteleconference user via a first logical channel and to the telephone setof a second adjacent teleconference user via a second logical channel.4. A method as defined in claim 3 further comprising the steps ofencrypting the transmitted calls of each of said first and secondlogical channels, thereby providing an outgoing secure call from oneuser to each adjacent user and decrypting each incoming secure call oncereceived at each user via said first and second logical channels, suchthat a secure teleconference network is provided between teleconferenceusers.
 5. A method of providing a teleconference call between a numberof users, comprising the steps of:instructing a communications networkhaving switching nodes and transmission links to establish a chain-likeconnection pattern between said users, by connecting the telephone setof a user to the telephone set of a first adjacent user via a firstlogical channel and to the telephone set of a second adjacent user via asecond logical channel; receiving a first incoming signal from a firstadjacent teleconference user via a first logical channel; decoding saidfirst incoming signal to provide a first incoming speech signal;forwarding said first incoming speech signal to a first input of asignal processing circuit means; receiving a second incoming signal froma second adjacent teleconference user via a second logical channel;decoding said second incoming signal to provide a second incoming speechsignal; forwarding said second incoming speech signal to a second inputof said signal processing circuit means; detecting the presence of anddecoding a user's output speech signal from an output of user interfacemeans; forwarding said output speech signal if present to a third inputof said signal processing circuit means; summing said speech signals ofsaid first and second inputs at said signal processing means andforwarding the summed signal to an input of code translation circuitmeans for conversion and forwarding to an input of said user interfacemeans; summing said speech signals of said second and third inputs atsaid signal processing means to provide a first outgoing speech signal;coding said first outgoing speech signal to provide a first outgoingsignal; transmitting said first outgoing signal to said first adjacentuser via said first logical channel; summing said speech signals of saidfirst and third inputs at said signal processing circuit means toprovide a second outgoing speech signal; coding said second outgoingspeech signal to provide a second outgoing signal; and transmitting saidsecond outgoing signal to said second adjacent user via said secondlogical channel.
 6. A method as defined in claim 5 further comprisingthe steps of encrypting the transmitted calls of each of said first andsecond logical channels, thereby providing an outgoing secure call fromone user to each adjacent user and decrypting each incoming secure callonce received at each user via said first and second logical channels,such that a secure teleconference network is provided betweenteleconference users.
 7. A method of bridging teleconference calls ateach telephone set used within a secure teleconference network,comprising the steps of:receiving a first incoming secure signal from afirst adjacent teleconference user via a first logical channel;decrypting said first incoming secure signal; decoding said decryptedfirst incoming signal to provide a first incoming speech signal;forwarding said first incoming speech signal to a first input of asignal processing circuit means; receiving a second incoming signal froma second adjacent teleconference user via a second logical channel;decoding said second incoming signal to provide a second incoming speechsignal; forwarding said second incoming speech signal to a second inputof said signal processing circuit means; detecting the presence of anddecoding a user's output speech signal from an output of user interfacemeans; forwarding said output speech signal if present to a third inputof said signal processing circuit means; summing said speech signals ofsaid first and second inputs at said signal processing means andforwarding the summed signal to an input of code translation circuitmeans for conversion and forwarding to an input of said user interfacemeans; summing said speech signals of said second and third inputs atsaid signal processing means to provide a first outgoing speech signal;coding said first outgoing speech signal to provide a first outgoingsignal; encrypting said first outgoing signal to provide a firstoutgoing secure signal; transmitting said first outgoing secure signalto said first adjacent user via said first logical channel; summing saidspeech signals of said first and third inputs at said signal processingcircuit means to provide a second outgoing speech signal; coding saidsecond outgoing speech signal to provide a second outgoing signal;encrypting said second outgoing signal to provide a second outgoingsecure signal; and transmitting said second outgoing secure signal tosaid second adjacent user via said second logical channel.
 8. A methodas defined in claim 7 further comprising the step of instructing acommunications network having switching nodes and transmission links toestablish a chain-like connection pattern between said teleconferenceusers such that each telephone set is connected to an adjacent setallowing each user to communicate with an adjacent user.
 9. A method asdefined in claim 8 wherein said communications network is instructed toestablish a chain-like connection pattern between said teleconferenceusers by connecting the telephone set of a user to a telephone set of afirst adjacent teleconference user via said first logical channel and tothe telephone set of a second adjacent teleconference user via saidsecond logical channel.
 10. A method of providing a secureteleconference call between a number of users, comprising the stepsof:instructing a communications network having switching nodes andtransmission links to establish a chain-like connection pattern betweensaid users, thereby allowing each user to communicate with an adjacentuser; receiving a first incoming secure signal from a first adjacentteleconference user via a first logical channel; decrypting said firstincoming secure signal; decoding said decrypted first incoming signal toprovide a first incoming speech signal; forwarding said first incomingspeech signal to a first input of a signal processing circuit means;receiving a second incoming signal from a second adjacent teleconferenceuser via a second logical channel; decoding said second incoming signalto provide a second incoming speech signal; forwarding said secondincoming speech signal to a second input of said signal processingcircuit means; detecting the presence of and decoding a user's outputspeech signal from an output of user interface means; forwarding saidoutput speech signal if present to a third input of said signalprocessing circuit means; summing said speech signals of said first andsecond inputs at said signal processing means and forwarding the summedsignal to an input of code translation circuit means for conversion andforwarding to an input of said user interface means; summing said speechsignals of said second and third inputs at said signal processing meansto provide a first outgoing speech signal; coding said first outgoingspeech signal to provide a first outgoing signal; encrypting said firstoutgoing signal to provide a first outgoing secure signal; transmittingsaid first outgoing secure signal to said first adjacent user via saidfirst logical channel; summing said speech signals of said first andthird inputs at said signal processing circuit means to provide a secondoutgoing speech signal; coding said second outgoing speech signal toprovide a second outgoing signal; encrypting said second outgoing signalto provide a second outgoing secure signal; and transmitting said secondoutgoing secure signal to said second adjacent user via said secondlogical channel.
 11. A method as defined in claim 10 wherein saidcommunications network is instructed to establish a chain-likeconnection pattern between said teleconference users by connecting thetelephone set of a user to a telephone set of a first adjacentteleconference user via said first logical channel and to the telephoneset of a second adjacent teleconference user via said second logicalchannel.
 12. A method of bridging teleconference calls at each telephoneset used within a teleconference network, comprising the stepsof:receiving an incoming call having multiplexed first and secondsignals from a communications network having switching nodes andtransmission links; demultiplexing said incoming call to provide saidfirst and second signals; decoding said first and second calls toprovide first and second incoming speech signals; summing said first andsecond incoming speech signals and forwarding the sum to a userinterface; detecting the presence of an output speech signal from saiduser interface; summing said first incoming speech signal with saidoutput speech signal to provide a first outgoing speech signal; summingsaid second incoming speech signal with said output speech signal toprovide a second outgoing speech signal; coding said first and secondoutgoing speech signals to provide first and second outgoing signals;multiplexing said first and second outgoing signals; and transmittingsaid multiplexed outgoing signals via a channel to said communicationsnetwork for connection to other teleconference users.
 13. A method asdefined in claim 12 further comprising the steps of encrypting saidfirst and second outgoing signals, thereby providing first and secondoutgoing secure signals and decrypting first and second incoming securesignals, such that a secure teleconference network is provided betweenteleconference users.
 14. A method as defined in claim 13 furthercomprising the steps of:instructing conference control means todemultiplex said transmitted outgoing signals from each of saidteleconference user once received at said communications network toprovide a first and second signal; instructing conference control meansto establish a chain-like connection pattern with said first and secondsignals, between said teleconference users, such that each telephone setis connected to an adjacent set allowing each user to communicate withan adjacent user; multiplexing said first and second signals that havebeen channelled for a particular teleconference user; and transmittingsaid multiplexed signals to said particular teleconference user via saidcommunications network.
 15. A telephone set useable for bridgingconference calls when used within a teleconference network,comprising:means for decoding a first incoming signal to provide a firstincoming speech signal; means for decoding a second incoming signal toprovide a second incoming speech signal; user interface means having aninput and an output; means for detecting the presence of and decoding auser's output speech signal from the output of said user interfacemeans; signal processing circuit means having a first and a second inputfor receiving said first and second incoming speech signal and a thirdinput for receiving said output speech signal; first means at saidsignal processing means for summing said first and second speech signalsto provide a first summed signal; code translation circuit means forconversion of said first summed signal and for forwarding to the inputof said user interface means; second means at said signal processingmeans for summing said speech signals of said second and third inputs toprovide a first outgoing speech signal; first means for coding saidfirst outgoing speech signal to provide a first outgoing signal fortransmission to a first adjacent user; third means at said signalprocessing means for summing said speech signals of said first and thirdinputs to provide a second outgoing speech signal; and second means forcoding said second outgoing speech signal to provide a second outgoingsignal for transmission to a second adjacent user.
 16. A telephone setas defined in claim 15 wherein said decoding means is provided with afirst and second input means for receiving a first and second incomingcall from a first and second teleconference user via a first and secondlogical channel and a first and second output means for providing afirst and second incoming speech signal.
 17. A telephone set as definedin claim 16 wherein said coding means is provided with a first andsecond input means for receiving a first and second outgoing speechsignal and a first and second output means for providing a first andsecond outgoing call for transmission to a first and secondteleconference user via said first and second logical channels.
 18. Atelephone set as defined in claim 17 wherein said first summing meanscomprises a first adder adapted to add the incoming speech signals fromsaid first and second outputs of said decoding means, said first adderhaving an output connected to the input of said user interface.
 19. Atelephone set as defined in claim 18 wherein said second summing meansfurther comprises a second adder adapted to add the incoming speechsignal from the first output of said decoding means to the outgoingspeech signal of said user interface, said second adder having an outputconnected to the second input of said coding means for transmission fromthe second output thereof to said second teleconference user via saidsecond logical channel.
 20. A telephone set as defined in claim 19wherein said summing means further comprises a third adder adapted toadd the incoming speech signal from the second output of said decodingmeans to the outgoing speech signal of said user interface, said thirdadder having an output connected to the first input of said coding meansfor transmission from the first output thereof to said firstteleconference user via said first logical channel.
 21. A telephone setas defined in claim 20 further comprising switching network means forestablishing a chain-like connection pattern between teleconferenceusers, such that each user communicates with a user of an adjacent set,each input and each output of said decoding and coding meansrespectively, being connected to said network means.
 22. A telephone setas defined in claim 21 further comprising conference control means forrequesting, setting-up and supervising the interconnection of saidteleconference users through said switching network means.
 23. Atelephone set as defined in claim 22 further comprising encrypting meansconnected at the output of said coding means for encrypting saidoutgoing call to provide an outgoing secure call and decrypting meansconnected at the input of said decoding means for decrypting an incomingsecure call.
 24. A teleconference network for interconnecting a numberof telephone sets, comprising:communications network means havingswitching nodes and transmission links for establishing a chain-likeconnection pattern between said telephone sets, such that eachteleconference user communicates with a user of an adjacent set; eachtelephone set being comprised of: means for decoding a first incomingsignal to provide a first incoming speech signal; means for decoding asecond incoming signal to provide a second incoming speech signal; userinterface means having an input and an output; means for detecting thepresence of and decoding a user's output speech signal from the outputof said user interface means; signal processing circuit means having afirst and a second input for receiving said first and second incomingspeech signals and a third input for receiving said output speechsignal; first means at said signal processing means for summing saidfirst and second speech signals to provide a first summed signal; codetranslation circuit means for conversion of said first summed signal andfor forwarding to the input of said user interface means; second meansat said signal processing means for summing said speech signals of saidsecond and third inputs to provide a first outgoing speech signal; firstmeans for coding said first outgoing speech signal to provide a firstoutgoing signal for transmission to a first adjacent user; third meansat said signal processing means for summing said speech signals of saidfirst and third inputs to provide a second outgoing speech signal; andsecond means for coding said second outgoing speech signal to provide asecond outgoing signal for transmission to a second adjacent user; andconference control means for requesting, setting-up and supervisinginterconnections of said telephone sets through said communicationsnetwork means.
 25. A teleconference network as defined in claim 24wherein said decoding means is provided with a first and second inputmeans for receiving a first and second incoming call from a first andsecond teleconference user via a first and second logical channel and afirst and second output means for providing a first and second incomingspeech signal.
 26. A teleconference network as defined in claim 25wherein said coding means is provided with a first and second inputmeans for receiving a first and second outgoing speech signal and afirst and second output means for providing a first and second outgoingcall for transmission to a first and second teleconference user via saidfirst and second logical channels.
 27. A teleconference network asdefined in claim 26 wherein said first summing means comprises a firstadder adapted to add the incoming speech signals from said first andsecond outputs of said decoding means, said first adder having an outputconnected to the input of said user interface.
 28. A teleconferencenetwork as defined in claim 27 wherein said second summing means furthercomprises a second adder adapted to add the incoming speech signal fromthe first output of said decoding means to the outgoing speech signal ofsaid user interface, said second adder having an output connected to thesecond input of said coding means for transmission from the secondoutput thereof to said second teleconference user via said secondlogical channel.
 29. A teleconference network as defined in claim 28wherein said third summing means further comprises a third adder adaptedto add the incoming speech signal from the second output of saiddecoding means to the outgoing speech signal of said user interface,said third adder having an output connected to the first input of saidcoding means for transmission from the first output thereof to saidfirst teleconference user via said first logical channel.
 30. Ateleconference network as defined in claim 29 further comprisingencrypting means connected at the output of said coding means forencrypting said outgoing call to provide an outgoing secure call anddecrypting means connected at the input: of said decoding means fordecrypting an incoming secure call.
 31. A telephone set useable forbridging secure teleconference calls when used in a teleconferencenetwork, comprising:means for decrypting a first incoming secure callfrom a first teleconference user to provide a first incoming signal;means for decoding said first incoming signal to provide a firstincoming speech signal; means for decrypting a second incoming securecall from a second teleconference user to provide a second incomingsignal; means for decoding said second incoming signal to provide asecond incoming speech signal; user interface means having an input andan output; means for detecting the presence of and decoding a user'soutput speech signal from the output of said user interface means;signal processing circuit means having a first and a second input forreceiving said first and second incoming speech signal and a third inputfor receiving said output speech signal; first means at said signalprocessing means for summing said first and second speech signals toprovide a first summed signal; code translation circuit means forconversion of said first summed signal and for forwarding to the inputof said user interface means; second means at said signal processingmeans for summing said speech signals of said second and third inputs toprovide a first outgoing speech signal; first means for coding saidfirst outgoing speech signal to provide a first outgoing signal; meansfor encrypting said first outgoing signal to provide an outgoing securecall for transmission to another teleconference user; third means atsaid signal processing means for summing said speech signals of saidfirst and third inputs to provide a second outgoing speech signal;second means for coding said second outgoing speech signal to provide asecond outgoing signal for transmission to a second adjacent user; andmeans for encrypting said second outgoing signal to provide an outgoingsecure call for transmission to another teleconference user.
 32. Atelephone set as defined in claim 31 wherein said decrypting means isprovided with a first and second input means for receiving a first andsecond incoming secure call from a first and second teleconference uservia a first and second logical channel and a first and second outputmeans for providing a first and second incoming call.
 33. A telephoneset as defined in claim 32 wherein said encrypting means is providedwith a first and second input means for receiving a first and secondoutgoing call and a first and second output means for providing a firstand second outgoing secure call for transmission to a first and secondteleconference user via said first and second logical channels.
 34. Atelephone set as defined in claim 33 wherein said decoding means isprovided with a first and second input means for receiving said firstand second incoming calls from said first and second output means ofsaid decrypting means and a first and second output means for providinga first and second speech signal.
 35. A telephone set as defined inclaim 34 wherein said coding means is provided with a first and secondinput means for receiving a first and second outgoing speech signal anda first and second output means connected to said first and second inputmeans of said encrypting means for providing a first and second outgoingcall.
 36. A telephone set as defined in claim 35 wherein said firstsumming means comprises a first adder adapted to add the incoming speechsignals from said first and second outputs of said decoding means, saidfirst adder having an output connected to the input of said userinterface.
 37. A telephone set as defined in claim 36 wherein saidsecond summing means further comprises a second adder adapted to add theincoming speech signal from the first output of said decoding means tothe outgoing speech signal of said user interface, said second adderhaving an output connected to the second input of said coding means fortransmission from the second output thereof to the second input of saidencrypting means.
 38. A telephone set as defined in claim 37 whereinsaid third summing means further comprises a third adder adapted to addthe incoming speech signal from the second output of said decoding meansto the outgoing speech signal of said user interface, said third adderhaving an output connected to the first input of said coding means fortransmission from the first output thereof to the first input of saidencrypting means.
 39. A telephone set as defined in claim 38 furthercomprising communications network means having switching nodes andtransmission links for establishing a chain-like connection patternbetween teleconference users, such that each user communicates with auser of an adjacent set, each input and each output of said decoding andcoding means respectively, being connected to said network means.
 40. Atelephone set as defined in claim 39 further comprising conferencecontrol means for requesting, setting-up and supervising theinterconnection of said teleconference users through said communicationsnetwork means.
 41. A secure teleconference network for interconnecting anumber of secure telephone sets, comprising:communications network meanshaving switching nodes and transmission links for establishing achain-like connection pattern between said secure telephone sets, suchthat each teleconference user communicates with a user of an adjacentset; each secure telephone set being comprised of: means for decryptinga first incoming secure call from a first teleconference user to providea first incoming signal; means for decoding said first incoming signalto provide a first incoming speech signal; means for decrypting a secondincoming secure call from a second teleconference user to provide asecond incoming signal; means for decoding said second incoming signalto provide a second incoming speech signal; user interface means havingan input and an output; means for detecting the presence of and decodinga user's output speech signal from the output of said user interfacemeans; signal processing circuit means having a first and a second inputfor receiving said first and second incoming speech signal and a thirdinput for receiving said output speech signal; first means at saidsignal processing means for summing said first and second speech signalsto provide a first summed signal; code translation circuit means forconversion of said first summed signal and for forwarding to the inputof said user interface means; second means at said signal processingmeans for summing said speech signals of said second and third inputs toprovide a first outgoing speech signal; first means for coding saidfirst outgoing speech signal to provide a first outgoing signal; meansfor encrypting said first outgoing signal to provide an outgoing securecall for transmission to another teleconference user; third means atsaid signal processing means for summing said speech signals of saidfirst and third inputs to provide a second outgoing speech signal;second means for coding said second outgoing speech signal to provide asecond outgoing signal for transmission to a second adjacent user; meansfor encrypting said second outgoing signal to provide an outgoing securecall for transmission to another teleconference user; and conferencecontrol means for requesting, setting-up and supervising theinterconnections of said secure telephone sets through saidcommunications network means.
 42. A secure teleconference network asdefined in claim 41 wherein said decrypting means is provided with afirst and second input means for receiving a first and second incomingsecure call from a first and second teleconference user via a first andsecond logical channel and a first and second output means for providinga first and second incoming call.
 43. A secure teleconference network asdefined in claim 42 wherein said encrypting means is provided with afirst and second input means for receiving a first and second outgoingcall and a first and second output means for providing a first andsecond outgoing secure call for transmission to a first and secondteleconference user via said first and second logical channels.
 44. Asecure teleconference network as defined in claim 43 wherein saiddecoding means is provided with a first and second input means forreceiving said first and second incoming calls from said first andsecond output means of said decrypting means and a first and secondoutput means for providing a first and second speech signal.
 45. Asecure teleconference network defined in claim 44 wherein said codingmeans is provided with a first and second input means for receiving afirst and second outgoing speech signal and a first and second outputmeans connected to said first and second input means of said encryptingmeans for providing a first and second outgoing call.
 46. A secureteleconference network as defined in claim 45 wherein said first summingmeans comprises a first adder adapted to add the incoming speech signalsfrom said first and second outputs of said decoding means, said firstadder having an output connected to the input of said user interface.47. A secure teleconference network as defined in claim 46 wherein saidsecond summing means further comprises a second adder adapted to add theincoming speech signal from the first output of said decoding means tothe outgoing speech signal of said user interface, said second adderhaving an output connected to the second input of said coding means fortransmission from the second output thereof to the second input of saidencrypting means.
 48. A secure teleconference network as defined inclaim 47 wherein said third summing means further comprises a thirdadder adapted to add the incoming speech signal from the second outputof said decoding means to the outgoing speech signal of said userinterface, said third adder having an output connected to the firstinput of said coding means for transmission from the first outputthereof to the first input of said encrypting means.
 49. A telephone setuseable for bridging conference calls when used in a teleconferencenetwork, comprising:means for demultiplexing an incoming call havingmultiplexed first and second signals received from a communicationsnetwork having switching nodes and transmission links; means fordecoding said first and second incoming signals to provide a first andsecond incoming speech signal; first means for summing said first andsecond incoming speech signals; user interface means having input meansfor receiving said incoming speech signals; means for detecting thepresence of an outgoing speech signal from an output of said userinterface means; second means for summing said first incoming speechsignal with said outgoing speech signal to provide a first outgoingspeech signal; third means for summing said second incoming speechsignal with said outgoing speech signal to provide a second outgoingspeech signal; means for coding said first and second outgoing speechsignals to provide a first and second outgoing signal; and means formultiplexing said first and second outgoing signals for transmission viaa logical channel to a switching network for channelling to anotherteleconference user.
 50. A telephone set as defined in claim 49 furthercomprising means for encrypting said first and second outgoing signals,thereby providing first and second outgoing secure signals and means fordecrypting first and second incoming secure signals, such that a secureteleconference network is provided between teleconference users.
 51. Atelephone set as defined in claim 50 further comprising:conferencecontrol means for demultiplexing said transmitted outgoing signals fromeach of said teleconference user once received at said switching networkto provide a first and second network signal, for establishing achain-like connection pattern of said network signals, between saidteleconference users, such that each telephone set is connected to anadjacent set allowing each user to communicate with an adjacent user,for multiplexing network signals that have been channelled for aparticular teleconference user, and for transmitting said multiplexednetwork signals to said particular teleconference user via saidswitching network.